同位体水(H 2O,D 2O)に対するZr-V-Feの排気作用

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Recovery and storage of tritiated water is one of the important problems for the safe handling of large amounts of tritium, because it is anticipated that a considerable amount of tritium becomes tritiated water once tritium is introduced into the handling system. From this viewpoint, we have studied the absorption/desorption phenomena of water (H2O and D2O) for Zr-V-Fe getter (St-707, SAES Getters) by means of mass analyzed thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry. The absorption rate of water vapor changed linearly with exposure pressure. The activation energies and frequency factors were determined as Ea(H2O)=1.8kcal/mol and νa(H2O)=2.1cc/sec・cm2 (projected area), and Ea(D2O)=2.7kcal/mol and νa(D2O)=4.0 cc/sec・cm2 (projected area), respectively. Only hydrogen molecules (H2 or D2) was desorbed when the getter was heated after exposure to water. The desorption obeyed second order kinetic with respect to the amount of water absorption. The activation energies and frequency factors were the same as those observed for desorption of hydrogen after hydrogen exposure. The XPS analysis made it clear that the surface mainly consisted of metallic Zr and V; a part of them, however, was oxidized due to exposure to water. In the SIMS measurement, ZrOD+, VOD+, VOD+2, and OD- peaks appeared after exposure to D2O vapor. The intensities of these peaks and intensities of the oxide peaks of Zr3d5/2 and V2p3/2 decreased as the exposure temperature increased. It was concluded that: (1) the rate determining steps for the absorption and desorption were the surface decomposition reaction of adsorbed water molecules or hydroxyl groups and surface association reaction of hydrogen atoms diffused to the surface from the bulk; (2) both Zr and V work as active sites for absorption where the Zr-site plays a more important role than the V-site; and (3) the Zr-V-Fe getter is suitable for the recovery and storage of tritiated water as well as tritium gas.
富山大学の論文

同位体水(H 2O,D 2O)に対するZr-V-Feの排気作用

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